Tools, specifically dressable grinding tools, have to be balanced to achieve high-quality work results. Depending on whether the tool arbor has one or more disc-shaped tools and/or one or more cylindrical tools, the tools may be balanced in one balancing plane or in two balancing planes.
Imbalances are rotary forces which arise with rotating bodies when the masses of the rotating bodies are asymmetrically distributed about a center. If a body rotates about an axis of rotation, outwardly acting centrifugal forces arise. If the mass is uniformly distributed in the rotational body, the centrifugal forces cancel each other out and the body remains in situ during the rotation. If, in contrast, the mass is unevenly distributed, additional forces and torques act on the body which cause a relative movement of the rotational body with respect to the axis of rotation. As a result, if the body is fixed into position by a bearing, strain may arise on the bearing.
There are two types of imbalance which can also occur in combination, namely static and dynamic imbalances. If the mass body is seen as a small slim disk having a mass the centers of mass are at the same spacing n and in the same direction with respect to the axis of rotation. This has the consequence with a static imbalance that the center of mass of the rotational body does not lie on the axis of rotation, but rather that the central principal axis of inertia is parallel at a spacing e from the axis of rotation. Centrifugal forces thus act perpendicular to the axis of rotation while the mass body rotates and can no longer be compensated. The imbalance Ui is produced which is defined as the product of the point mass mi and its spacing ri from the axis of rotation. This static imbalance can be measured in a stationary state. For example, an imbalance scale can measure the static imbalance of grinding wheels.
With a dynamic imbalance, the center of mass of the rotational body lies on the axis of rotation, but the principal axis of inertia is at an angle relative to the axis of rotation. The reason for this is that the center of mass of the individual discs does not lie on the axis of rotation. Considered on their own, these small discs therefore have centrifugal forces generating an imbalance. The imbalance forces admittedly add up to zero, i.e. no forces are produced in a lateral direction; however, since they lie on parallel lines of application, they result in a moment load acting on the rotational body. A so-called bending moment therefore arises during the rotation. A non-uniform wobbling rotational movement is produced as a result. The dynamic imbalance can only be measured with a rotating rotational body. With technical rotational bodies, a general dynamic imbalance is typically present, i.e. a combination of static and dynamic imbalance.
An imbalance in tool holders arises when defects in design, drawing, material, production or installation are present. In addition to the named defects, imbalances can furthermore occur with dressable grinding tools due to different material densities or different amounts of coolant flowing to the grinding tool.
Tools having a large amount of imbalance have a negative effect on many aspects of machining. For example, an imbalanced tool may produce a poorer surface quality in machined workpieces due to vibrations at a tool holder holding the tool, oscillations at the tool holder, a restriction of achievable cutting speeds, reduced production accuracy, and/or increased down time of the tools due to uneven blade wear.
To avoid these negative effects, it is recommended to balance the tool holder or, even better, to balance the tool holder with clamped tool, in accordance with technically feasible and economically meaningful balance quality. During balancing, the asymmetrical mass distribution of the tool holder is compensated in that either mass is attached, mass is removed or mass is displaced. It is the aim of the balancing to restrict bearing forces, bearing vibrations and wave deformations to acceptable values.
To compensate an imbalance, it must first be analytically determined using measurement processes. The centrifugal forces which occur are measured by means of vibration sensors and the imbalance and the required imbalance compensation are calculated. The required adaptations at the tool system are then carried out using data. Such tools are balanced either on a separate balancing machine and/or on the manufacturing machine. Tools which are dressed on a manufacturing machine also change their balance state due to the dressing process. It is therefore always advantageous in such a case to balance these tools still on the manufacturing machine.
Attempts to address imbalance include a balancing system European Patent No. 1 870 198 A1. Therein, a balancing system for balancing a grinding wheel is shown which is arranged directly below the grinding tool in the tool arbor. The balance state of the tool is detected via a corresponding sensor system and is evaluated by a processing unit. Control signals are output to the balancing unit as the result of the evaluation to adjust the balancing weights accordingly.
However, the inventors herein have recognized potential issues with such systems. As one example, such systems are well-suited for wide tools and large worm diameters since the tool bore is dimensioned sufficiently, and the tool arbor offers sufficient room for the accommodation of the balancing heads. However, as the available space is reduced, the size of the balancing weights used and the maximum compensable imbalance are also reduced. Large imbalances must, however, in particular often be corrected with fast-turning tools.
If furthermore workpieces are to be machined which are collision-prone, the use of grinding worms having very small diameters or of grinding wheels with very small grinding wheel diameters or a combination of the two is necessary. These systems generally are not appropriate for tools with very small diameters since the tool arbor for receiving the grinding tools has to have a certain minimum diameter for receiving the balancing head.
The object of the present application is to provide an innovative construction of a machining head for a gear generating machine, the machining head comprising a balancing system for small-dimension tools or tool arbors for the gear machining or machining in this manner of workpieces which are in particular collision prone. These small tool diameters are selected when otherwise too large a tool diameter would produce an unwanted collision between the tool and diameters adjacent to the gearing or further gearings at the workpiece.
This object is achieved by a machining head for a gear manufacturing machine, comprising: at least one driven motor spindle including at least one balancing device integrated within the at least one driven motor spindle; at least one counter-spindle including at least one balancing device integrated within the at least one counter-spindle; and a tool arbor having at least one tool arranged thereon mounted between the motor spindle and the counter-spindle.
In accordance with the present disclosure, a machining head for a gear manufacturing machine is proposed which comprises at least one driven motor spindle for receiving a tool arbor. A balancing device for correcting imbalances of the received tool is integrated in accordance with the present disclosure within the driven motor spindle. The tool arbor is received at both sides, i.e., on the one hand, by the motor spindle, and on the other hand, by an oppositely disposed counter-spindle. The counter-spindle also comprises at least one integrated balancing device. The balancing devices of the motor spindle and of the counter-spindle preferably comprise balancing weights or balancing heads whose positions can be adjusted to compensate an imbalance (e.g., the components distributed over the motor spindle and the counter-spindle can form a common two-plane balancing system for compensating an imbalance).
The integration of the balancing device into the motor spindle or counter-spindle allows the reception of different tool arbors or the use of different tools independently of their diameters. Tools, in particular grinding wheels or grinding worms, having very small diameters can thereby be used in particular to manufacture gears on workpieces prone to collisions. The minimum tool bore diameter in this respect depends on the required balancing capacity to be achieved. The greater the required capacity, the greater the mounting bore for the balancing system has to be. In this respect, tool bore diameters below 50 mm are, for example, no longer suitable to integrate a conventional balancing system in accordance with the prior art into the tool arbor.
Not only the use of different tool arbors having particularly small diameters is made possible by the integration of the balancing devices within the motor spindle or counter-spindle, but any projecting edges are also omitted which possibly arise due to the arrangement of the balancing devices at or around the tool arbor. The integrated balancing devices in particular do not influence the possible shift path of the tool or of the tool arbor in the V direction, i.e. along the axis of rotation of the tool. This is in particular of advantage in gear manufacturing machining or gear grinding machining since here different regions of a tool are brought into engagement with the workpiece by a shift in the direction of the V axis. It is likewise conceivable to arrange a plurality of the same tools or also of different tools on the tool arbor such as a grinding wheel or a grinding worm which can be alternately brought into engagement with the workpiece by a shift movement. The complete integration of the balancing devices within the motor spindle or the counter-spindle does not influence the maximum shift movement.
The balancing devices of the motor spindle and/or of the counter-spindle are ideally completely or at least almost completely encompassed within the housing of the motor spindle or of the counter-spindle. For example, the balancing device of the motor spindle can be arranged within the rotor, while the balancing device of the counter-spindle is within the spindle shaft rotatably supported there.
The balancing devices of the motor spindle and/or counter-spindle can each comprise one or more balancing weights, for example, which are adjustable in the radial direction of the respective spindle so that compensation can take place by radial displacement of the balancing weights in dependence on the measured vibrations. An embodiment is likewise conceivable having a plurality of radially arranged chambers having different liquid quantities. The balance state of the spindles can be varied by a controlled variation of the filling level of the liquid chambers.
An alternative embodiment of the balancing device can be based on at least one balance weight per balancing device/balancing plane, which is electromechanically adjustable about the middle axis by means of at least one motor. A balancing in two balancing planes can thereby be implemented.
An arrangement of the balancing device within the motor spindle or within the counter-spindle behind or below the front spindle bearing is particularly preferred. The front spindle bearing corresponds to the bearing which is arranged spatially closer to the tool arbor.
At least one vibration sensor, preferably at least one acceleration sensor, is provided to detect any imbalances, ideally a vibration sensor per balancing plane and thus respectively one for the motor spindle and a further vibration sensor for the counter-spindle. The vibration sensors preferably serve the recording of the vibrations during gear manufacturing machining, ideally vibrations of the total system of tool arbor, received tools and spindles. The vibration sensors can preferably be in communication with a control. The control determines control pulses for setting the balancing systems from the vibration signals, said control pulses having to be transmitted contactlessly via signal transmitters into the balancing devices.
One or more signal transmitters can be provided to transmit the correction signal determined in the control back to the balancing device after the imbalance signals have been converted into correction values within the control. The signal transmitters can, for example, be arranged at the rear end, i.e. at the end disposed opposite the tool arbor, of the motor spindle or of the counter-spindle.
The machining head can in particular be designed such that the spacing between the counter-spindle and the motor spindle can be variably set. The machining head can thereby be usable for different tool lengths in that it is variably adjustable per tool length or tool arbor length. This flexible configuration possibility first arises in that the balancing device is encompassed in the motor spindle or in the counter-spindle and is not attached to or in the tool arbor itself.
The machining head is in particular dimensioned for very small grinding wheels or small grinding worms. Such small-dimension tools are preferably operated at high speeds of revolution. The motor spindle is accordingly preferably designed for a spindle speed of more than 8,000 revolutions per minute.
In addition to the machining head, the present disclosure likewise relates to a gear manufacturing machine for grinding gearings using at least one machining head in accordance with the present disclosure or with an advantageous embodiment of the present disclosure. The gear manufacturing machine is consequently characterized by the same advantages and properties as the machining head in accordance with the present disclosure so that a repeat description is omitted at this point.
The gear manufacturing machine comprises at least one control which can be communicationally connected to one or more vibration sensors and signal transmitters of the machining head or corresponding evaluation electronics. The control is in particular suitable for receiving one or more vibration parameters from the vibration sensors and for generating corresponding adjustment values for the one or more balancing devices of the motor spindle and/or counter-spindle in dependence on the received vibration parameters. The control parameters are ideally likewise generated in dependence on the current spindle speed of the motor spindle and/or on the current angular position of the motor spindle/counter-spindle to compensate imbalances detected by means of the vibration sensors.
Further advantages and properties of the present disclosure will be explained in more detail in the following with reference to various embodiments.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.
FIGS. 1-4 are shown to scale, though other relative dimensions may be used.